Telephone system



June 3, 1930. v. s. THARP TELEPHONE sysl'wEm Original FiledApril so, 1927 53km :llll n S v6 ww v H W Y SS Y IIIIIIIIIIIIIIL T FL.

- Inueu or Um SThEr Patented June: 3, 1930 aria-emissvrcron s. mean, or nrnrrnnsnlrniirncrs, essrenonlro nnsnnvn no rinrne con- :eAnY, on Kansas crrnnrssonnr, a con-renames: OEDELAWARE I TELEP ONE srs'rn a Application filed April so, 1927, Serial no. 127,745. Renewed August3Q,19 29.

located approximately halfway between two larger exchanges is only connected to one of the largerexc-ha-nges by trunk lines comprising iron wires while the two larger exchanges are connected together by "direct through toll lines. Connections from the small exchange, hereafter designated. ex-

change No. 2, to the nearest large exchange,

hereafter designatecl'exchange No. '1, are completed over the trunk lines connecting exchange No. 2 withexchange No. 1. In view of-the fact that there are no direct trunk lines extending from the small exchange, or exchange N0. 2, to the more distant large exchange, or exchange No. 3,,connections between exchange No. 2 and exchange No. 3 must be set up or controlled over the trunk lines connecting the exchange No. 2 to the exchange No. land then over the through toll/lines to exchange No. 3, although the through toll lines pass fairly close to the smallexchange. "The small exchange is not normally connected to the through toll lines because such connections, if permanently connected in bridge of the toll lines, would greatly impair the transmission over such toll lines when they are used for connections between exchange No. 1 and exchange No. 2, and points beyond.

Accordingly, the main object of the' in vention maybe saidto consist in-the provision of'means for improving the toll transmission on toll connections between the small exchange and exchange No. 3. This is done by temporarily connecting the subscribers lines at the small exchange to the through toll lines at a point where such toll lines pass near the smalleexchange By this arrangement the length of wire in the talking circuits is greatly reducedand the quality of the circuits is correspondingly, improved. A feature of the invention relates to the novel circuit arrangement by meansof which the connections to the through: toll-lines at the'small exchange are controlledat the will of the toll operator at exchange'No. 1. v

a A further feature relates to the circuit arrangement by means of which night service can be furnishedrto a particular subscriber whose line terminates in the smallexchange when the operator at the small exchangehas left her position after working hours.

Various other features w1ll be POIIICSCl OUt' inthe detailed specification which follows.

Referringwnowto the drawing there is shown by means of the usual circuit diagrams sufficient of'the 'apparatus used-to f enable the invention derstood. .e 1 I In the upper part of the drawing there'are shown thelconductors of one phantomxarid two physical through toll lines extending to be described and unbetween two distant exchanges indicated as exchanges No; I and No. 3. 1 These'through toll lines terminate at. one end in repeating coils and jacks such asrepeating coil R and jack J in exchange No. 1 rand atgthe other end in repeating coils and jacks such as repeating coil B and jack J in exchange No. 3. The toll lines 1 and 2 are connected in phantom at exchanges No. 1-1 and Noz-x-3, thereby providing the thirdtoll line or toll line 3 between the exchanges.

. Approximately half way between v I exchanges No; 1 and N0. 2 thethrough toll lines pass at their nearest point within one thousand feet or so of a small rural exchange indicated as exchange N0. 2. At this point a cable box, indicated by the dotted rectangle in the upperand center portion ofthe draw ing, is mounted on one of the poles of the toll lineand a cable comprising the conductors 11 to 16, inclusive, connects the apparatus in the cable box with thejapparatus in exchange N0. 2. o In, the lower left-hand part ofthedrawing there isrshown the conductors of one phantom and two physical trunk lines extending between exchange No. 1 and exchange N 0.. 2. These trunk lines terminateat one end in repeating 0011s and yacks'such asrepeating 0011 R and gack'J in exchange No.

1 and in the other end. in repeating coils and jackssuch as repeating coil. R and jackJ in 7 made of iron wire and are connected in phantom at exchanges 1 and 2 thereby providing a third trunk line or trunk line No. 3 between the exchanges. Trunk line l lo. 3 is primarily for use as a dialing trunk and is equipped with a dial key K and a calling device CD by means of which the operator at exchange N o. 1 may operate the connector C in exchange N0. 2.. Cord circuits (not shown) are also provided at exchanges No. 1 and No. 3 for completing or extending toll connections.

In exchange No. 2 conductors 8 and 9 are connected to the left hand'windings of the repeating coil R for the purpose of controlling the connector C over the trunk line 3. The connector C may be briefly described as consisting of a pair of wipers and their associated bank contacts, together with a stepping magnet for advancing the switch wipers and a release magnet for restoring the switch to normal. The mechanical construction of the connector C is somewhat similar to the well known minor switch but the circuits have been modified in accordance with the present invention.

' Associated with theconneotor C-and connected to the respective bankcontacts in the banks of the connector there are shown three relays whose functions are to connect t e ring and tip conductors of the plug P to the secondary windings of the repeating co ls R and B when energized. The plug P is used by the operator at exchange No. 2 for completing toll calls to the local subscribers lines such as indicated at A. Associated with the plug P there is provided a ringing key RK for the purpose of enabling the operator to ring the called subscribers bell. The subscribers lines such as A are of the well known magneto type and terminate at exchange No. 2 in jacks such as jack J Cord circuits (not shown) are used by the operator at exchange 2 for completing calls between local subscribers.

A cable comprising conductors 11 to 16, inclusive, extends from exchange No. 2 to the cable box for the purpose of operating the relaystherein and to connect the primary windings of the repeating coils R and B to No. 3 to the tip and ring conductors of plug P fora purpose to be described hereinafter.

Having described in a general way the layout of the system herein disclosed, the operation of the circuits will now be described in detail, it being assumed for this purpose that a subscriber in exchange No. 3, or beyond, desires to converse with subscriber A in the small exchange, or exchange No. 2. It will further be assumed that an operator at exchange No. 3 has plugged into the ack J of the toll line 1 and has operated the drop D to signal the toll operator at exchange 1 in the well known manner. The toll operator at exchange 1 inserts the answering plug of a cord circuit (not shown) into the jack J. Upon ascertaining that a connection is desired to subscriber A in exchange 2, the toll operator at exchange 1 will insert the calling plug of the cord circuit into the jack J and operate the dial key K and then dial the digit 1 by operating the calling device CD.

Responsive to the operation of the dial key K in exchange 1 a circuit for operating the line relay 23 of the connector C in exchange 2 may be traced as follows: from ground by way of lower winding of line relay 23, lower winding of impedance coil 22, conductor 9, upper left-hand winding of repeating coil R trunk line No. 2, upper-right hand winding of the repeating coil R impulse springs of the calling device CD, key K, lower righthand winding of repeating coil R trunk line No. 1, lower left-hand winding of repeating coil R conductor 8, upper winding of impedance coil 22, to the upper winding of line relay 23 and battery. Line relay 23 energizes over the above traced circuit and closes a circuit for energizing the slow-to-release relay 24. Release relay 24, upon energizing, at armature 39 prepares the impulsing circuit and at armature 4O closes an energizing circuit for relay 21. At armatures 35 and 36 relay 21 shorts out the upper and lower windings of the impedance coil by connecting the upper and lower windings of the line relay direct to conductors 8 and 9. The impedance relay 22 is initially included in the circuits of the line relay 23 to prevent the battery and ground connections of the line relay from interfering with ringing current when the operator at exchange No. 1 desires to ring 1*.

over trunk line No. 3. During impulsing, however, the impedance relay 22 is shorted out by the operation of relay 21 as before described.

device CD in accordance with the digit 1, the circuit of the line relay is interrupted and said relay in falling back closes a circuit for operating series relay 26 and stepping magnet 27 as follows: ground by way of armature 37 and its resting contact, armature 39 and its working contact, armature 11, winding of relay 26, and winding of stepping magnet 27 to battery. Series relay 26 and the stepping magnet 27 are operated over the above tracedicirc'uita nd the series relay 26 at armature 14: closes a circuit for maintaining the impulsing circuit'findependent of. arma ture 41 of relay 25. .in case said why should energize. By the operation'ofthe stepping magnet 27 the switch wipers 15. and 46 are" stepped into engagement with the first bank 7 contacts? After the impulse, relay 23.1'6611- ergizes and opens the impulsing circuit at ar mature 37: Relay 24 being slow-acting therefore/maintains its armatures attracted be tween impulses. A short interval of time after the impulse the series relay 26', which 19.:trom the tip and ring conductors termi-f nating in jack J and are connected instead to the operators headset throughthe-normally closed springs .ofthe'night key NK.

The toll operator at exchange No. 1 now informs the operator atexchange No. 2 that a toll connection is des rediwith subscriber A whereup'on the operator. at exchange No. 2

inserts the plug P into the jackd associated with the line of'subscriber A. The operatorat exchange 2 operatesthe ring key BK associated with the plug P thereby ringing the bellon the. desired subscribers line in the well known manner; s

The toll operator atexchange No. 1 now releases the key K thereby opening the circuit of. line relay 23. Line relay 23, upon de- -energizing, opens the circuit of release relay 24 and the latter relay after an interval deenergizes.t.1 .-elease relay 24, upon deenergiz ing, at armaturet38 opens the circuit of relay 20and at armature 40 opens the circuit of I relay '21-whereupon} said relays deenergize.

At armature 39 the release relay'closes a-cir cui-t to release magnet 28 over a circuit in-' eluding armatu'res 37, 39, and 12. By the operation of release magnet 28 the switclr' wipers45 and46 are returned to their normal positions. f I i In case the operator at exchange No. 2

has. temporarily left'her position and has Well known manner. jAt armature 4 the drop D closes a circuit for operating an alarm not operated the night keyNK the toll operator at exchange 1 releases the connector switch as previously explained and operates a ringing key in her cord circuit (not shown) whereupon the drop D is operated in the signal in orderto informthe operator at 1 exchange 2 that a connection is desired.

The operator'atexchange 2 upon "hearing the alarn'i'signal returns to her posltion and inserts'the answerlng plug of a. cord circu t (not shown) into the jack J and converses.

with the distant operator in known manner after which she removes said plug and inserts the plug P into jack J if'a connection.

is desired to subseriberAQ The operator in exchange '2 now operates the ringing key RK and thereby ringing the bell on the called:

subscribers line. a

After giving the necessary instructions to the operatorin exchange 2 thextoll operator at exchange 1 again operatesthe key. K'theie by operating relays 23 and 24 as before. The

toll operator now operates-the calling device CD in accordance with the digits2, 3, 0r 4 dependent upon which toll lineis in use. In

toll operator will dial the digit 2 whereupon:

the connector C is operated as previously de-.; scribed with the exception that relay 30 'instead of relay 20 is operated when the series relay 26 deenergizes. gizing relay 30 may be traced as follows:

from ground by way of relay 33 in the cable The circuit for enerbox, conductor 12, winding of relay 30,:sec-

. ond bank contact accessible to wiperv 45. and

said wiper, armature38, and armature43 to 7 battery. Relay 33 also energizes over the above traced circuit and connects the primary windings of-the repeating coil R to the two conductors of the tollline No. 1. Relay 30, upon energizing-, at armatures 47 and 48 connects the secondary windings of the. repeatin'g coi l it to the ring and tip conductors of the plug P which are now in engagement with the line of subscriber A. At armature 49 relay 30 closesa locking circuiti or itself and relay 33 which includes the plugseat con- I tacts PS and the armature of relay 29. When the called subscriber answers the toll operator at exchange 1 converses with the called subscriber over toll line No. 1 by theaid eitherepeating coils R andR gThe calling subscriber being already connected to toll line No.1 the connection, therefore, between the calling and called subscr bers s .now comdesired. The established connectionis suno I Q pletedand such subscribers may converse as pervised over thetoll line No. 1 extending to the exchange'No, 1 independent of trunk line 3. r

When the desired connection is: completed the key' K whereupon theconnector releases in the samemanner as previously described.

Relays 30 and 33, however, are maintained energized over llhelflocking circuits and therefore do not deenergize when the 0011-" 'nector releases. f

the toll operator at exchangeNo. 1 releases 1.

When conversation is finished the toll operators at exchanges 1 and 3 remove the cord 85- this case, as the toll line Nolis in use, the;

circuits from the jacks J and .J The toll operator at exchange No. 1 operates the key K, and dials the digit 1 or rings the operator as previously described and tells her. to remove plug P from the jack of the called change 1 again releases the connector C and all apparatus used in establishing the connection is now in normal position.

Toll connections to toll line No. 2 stresstablished in the same manner only the digit 3 is dialed instead of the digit 2 and relays 31 and 34: are operated to connect up the repeating coil R to toll line No. 2. In case of a toll connection to the phantom circuit over toll line No. 3 the digit l is dialed whereupon relays 32, 33, and 3% are operated and establish a talking circuit to the phantom toll line in an obvious manner.

Toll calls originated at exchange No. 2 for exchange 3, or beyond, are handled in the following manner. A calling subscriber such as subscriber A desiring a toll connection operates his magneto at the substation thereby causing the drop D to operate and signal the operator at exchange 2. The operator thereat inserts the plug of a cord circuit (not shown) into jack J and when the operator learns that a toll connection, say to exchange 3, is desired she tells the party to hang up and that she will call back later. The operator at exchange 2 then inserts a calling plug of a cord circuit (not shown) into jack J and rings down the drop D to signal the operator at exchange 1 in known manner. The toll operator at exchange 1 answers by inserting the plug of a cord circuit (not shown) and after receipt of the information disconnects the plug from ack J and plugs into an idle toll line or waits until one becomes idle.

" When an idle toll line is available the toll operator at exchange 1 plugs into such line and signals the toll operator at exchange 3. The operator at exchange 3 after receiptof the desired information extends the call to the desired subscribers line. When the connection has been extended to the desired line the toll operator at exchange 1 is notified and she operates the key K and her calling dev1ce CD as previously described to connect with the 'operators headset 1n exchange No. 2. The

4: dependent upon which of thetoll lines is in ing subscriber is connected direct to the through toll line in the same manner as previously described.

In case the size of the small exchange, or exchange No. 2, is large enough so that two toll connections between exchanges No. 2 and N 0.3 are often desired at the same time a duplicate set of relays such as relays 20, 30, 31, 32,'and 29 would be provided to be controlled from the sixth to the tenth bank contacts, respectively, of the connector C in the same manner as relays 20, 30, 31, are controlled. Another plug and ringing key similar to plug P and ringing key RK would also be provided by means of which the connection to the subscribers line is completed. The toll operator at exchange No. 1 would then dial the digits necessary to operate the desired relay or relays in the duplicate set in order to make the proper connections to the desired toll line.

Having described how toll connections are completed when the operator at the small exchange is on duty, a description will now be given of the method for completing toll calls when the operator is absent, for instance during the night. In order to provide some sort of service during her absence, the operator inserts the plug P into the jackof some subscribers line which may be, by way of example, the telephone line of the local drug store or some other pay station and then operates her night key NK before leaving her position. For convenience it will be assumed that substation A is used for night service. The toll operators are informed that after a certain time the small exchange is unattended and therefore when a toll call is extended to exchange 1 for a subscriber in exchange 2 the operation is as follows: The toll operator now operates the key K and then the calling device CD in accordance with the digit 1 thereby opcrating the connector C and relay 20 as previously described. The toll operator new con? nects ringing current to the trunk line No.

3 by means of a ringing key in a cord circuit (not shown). The ringing circuit is repeated through the repeating coils R and R in an obvious manner and extends by way of armatures 18 and 19 and their working contacts through the normally open springs controlled by the now operated night key NK, conductors 5 and 6, through the normally closed springs of the ringing key RK, tip and ring of plug P tip and ring conductors of the subscribers line, and the bell of substation A.

l/Vhen the subscriber A answers, the toll operator advises him who the call is for and if the call is for subscriber A or a party who can be immediately called to the phone the toll operator is advised of the fact. The toll operator now releases relay 20 and connector C and thenreoperates the connector 0 to c0nnect the line of substation A to the through toll linein use in the same manner as pre-' tion A the toll operator is advised of the fact I by subscriber A. Subscriber Ahangsup his receiver and sends a messenger to inform the called subscriber that he is wanted at substation A to answer a tollcall. The tollopera-- tor removes the plug of her cord circuit (not shown) from J thereby bridging the drop D across trunk line No. 3. The toll-operator, however, in this instance 'does not release key K and therefore the connector C and relay 20 are maintained operated. When the desired called subscriber reaches; substation A said subscriber manually operates the magneto atsubstation A thereby operatingthe drop D at exchange No.- 1. Thetoll'operator, upon answering in known manner and ascertaining that the desired party is now at substation A, releases the key K, relay 20,

and connector C andcompletes the desired connection as previously described. The con nection now being completed the calling and called subscribers-may converse with each other as desired. 7

When conversation is finished the toll ,operator atexchangerNo. l dials the digit 5 whereupon the connector operates as before described and closes a circuit for' energizing relay 29 whichmay betracedas follows:

from ground byway. of the winding of relay 29, fifth bank contact accessible'to wiper and said wiper, armature 38, and armature .43

to battery. By the operation of relay 29 the locking circuit 'of'relays 3034=, inclusive,is opened and the operated" ones of saidrelays deenergize. The connector C'isagain released and all apparatus is returned to normal position. 7 I F. Local connections between. subscribers at 7 exchange No. 2 areconi-pleted by the attendant oroperator at suchexchange by-tl1e ;-aid;

ofcord circuits (not shown or by fthe call ing subscriber ringing thecode of thecalled subscriberwhen the desired called line is on thesame line. as the calling party; 00111198 tions between, subscribers -.lines; 'in exchangello. l and exchange N0. 2 arecompleted over the trunk-lines No. land No. 2 bythe-aid of cord circuits (not shown) vin the 'well' known manner, and therefore, need not be; explained p the operatorin said first exchange for'sigindetailh v i I v a, Having described the inventiomit's utility andoperation, what is consideredznew; and is desired: to have protected, bylietters- Patent V Hat a point between-saidnfirst and thirdex;

changes. I .1 I

5. In a telephone system, three exchanges, r p

will be set forth in the appended claimsr; 1';

That is claimed is 1. In a telephone system,

first exchange and-said third exchange, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, and meanswhereby said, trunk line is required to establish a particu-' lar toll connection between said second and: third exchanges but is excluded from the talking circuit when the toll connection is com.-. pleted, the talking circuit oftthe completed toll connection including inductive connections between the second exchange and a toll.-

line at a point near said second exchange.

2. In a telephone system, three exchanges,

throughtoll lines connecting said firstex change and said third exchange, said toll. lines passing close to but normally discons.

nected from said second'exchange, atrunk line connectingsaid first exchange with saidsecond exchange, relays associated with said toll lines at a point near said second exchange for inductively connecting said toll lines to 7 said second exchange and-means in said sec; ond exchange controlled over said trunk line at the will of the operatorin said first exchange for energizing'said relays. V 3. In a telephone system, three exchanges,- through toll lines connecting said first ex change andv said third exchange, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, relays associated. with said 1 toll lines at a pointnear said second exchange for inductively connecting said toll lines to branch lines terminating in said secondexchange, aconnector switch in said second ex-- change directively controlled over said trunk line at'thewill of the operator in-said'first exchange, means including a plug in said second exchange for completing a connection to a manual subscribers line terminating therein, means foroperatiiig said connector to energize said relays, andother means also operated by saidconnector for inductively connecting said 'plug to said branch lines,

:4. In a telephone system, three exchanges,- through toll lines connecting said'firstex-* changeIand'said third exchange, said to1llines passing close to but normally disconnected from said second eXchange,--a trunkj lineconnecting said first exchange with said secondexchange, a manual subscriber s line terminating my said secondexchange, 'means 1 V includinga plug n said second exchangeforservice, and-nieans controlled at the will of j nalling said subscriber oversaid trunklineand for inductively connecting SitldjSllbSCI'lb: ers line; to a desired oneof saidtoll l nes through. toll; lines connecting. said; first. ex=

connecting up said subscribers line forinight 7 to a desired one of said toll lines at a point between said first and third exchanges, means independent of control from said first exchange for maintaining said inductive connection, and means controlled at the will of the operator at said first exchange for causing said inductive connection to be opened.

6. In atelephone system, three exchanges, through toll lines connecting said first and third exchanges, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, and means controlled over said trunk line and at the will of the operator in the first exchange for causing said second exchange to be connected to any desired one of said toll lines at a point near said second exchange.

7. In a telephone system, three exchanges, through toll lines connecting said first and third exchanges, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, manual subscribers lines terminating in said second exchange, and means controlled over said trunk line for causing a predetermined one of said subscribers lines to be connected and discon'nectedto and fromany one of said toll lines at the will of the operator in the first exchange when said second exchange is unattended during the night.

8. In a telephonesystem, three exchanges, through toll lines connecting said first and third exchanges, said toll lines passing close to but normally disconnected from said sec-' ,ond exchange, a plurality of relays in said second exchange, each of said relays controls,

ling circuits for inductively connecting one of the toll lines to said second exchange, a locking circuit for maintaining said relays when energized-in operated position, and a connector switch in said second exchange,

said connector controlled over said trunk line by the operator in said first exchange to first, seleotlvely operate one of said relays tonductively connecta desired one of said -toll lines to-the second exchange at apoint lines and one phantom toll line, a subscribers line, a relay associated with each physical toll line, and means for selectively energizing either of said relays to inductively connect said subscribers line to the respective physical toll lines or both of said relays to inductively connect said subscribers line to said phantom toll line.

10. In a telephone system, three exchanges, through toll lines connecting said first exchange and said third exchange, said toll lines passing close to but normally disconnected from said second exchange, atrunk line connecting said first exchange with said second exchange, a connecting link in the second exchange, and means controlled by the operator in the first exchange over said trunk line for connecting said link with any one of said through toll lines.

11. In a telephone system, three exchanges, through toll lines connecting said first ex change and said third exchange, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, a plug ending'link circuit in the second exchange adapted to be connected with any subscrib'ers line in the second exchange, and means controlled by the operator in the first exchange over said trunk line for connecting said link circuit with any one of said through toll lines.

12. In a telephone system, three exchanges, through toll lines connecting said first exchange and said third exchange, said toll lines passing close to but normally disconnected from said second exchange, a trunk line connecting said first exchange with said second exchange, a connecting link in said second exchange, a plurality of relays, and means controlled by the operator in the first exchange over said trunk line for selectively operating desired combinations of said relays to inductively connect said link with any desired one of said through toll lines.

13. In a telephone system, a trunk line terminating in a line relay and a jack and drop, an impedance coil, a circuit for said line relay including said trunk line, said impedance coil, and said line relay in series, said impedance coil preventing said line relay from interfering with the operation ofsaid drop when ringing current is applied to said trunk line, means for closing said circuit to operate said line relay, and means responsive to the operation of said line relay for short circuiting said impedance coil thereby directly connecting said line relay with said trunk line.

14. In a telephone system, a repeating coil, a trunk lineterminating in said repeating coil,'a jack and a drop normally connected to said repeating coil, a'line relay, an impedance coil, a circuit for said line relay including' said impedance coil, said repeating coil, and said line relay in series, said impedance fering with the operation of said drop when ringing current is applied to said trunk line to operate said drop, means for closing said circuit to operate said linerelay, and means responsive to the operation of saidline relay for short circuiting said impedance coil thereby directly connecting said line relay with said repeating coil.

15. Ina telephone system, three exchanges, toll lines connecting said first exchange and said third exchange, a toll trunk line connecting said first exchange and'said second exchange, subscribers lines terminating in said second exchange, and means at said second exchange controlled over said trunk line at the will of the operator in the first exchange for connecting one of said subscribers lines to a desired one of said toll lines for talking purposes, p

16. In a telephone system, three exchanges, toll lines connecting said first exchange and said third exchange, a trunk line connecting said first exchange and said second exchange,

subscribers lines terminating in said second exchange, means at said second exchange con: trolled over said trunk line at the will of the operatorin the first exchange for connecting one of said subscribers lines to a desired one of said toll lines for talking purposes,'means for maintaining said connection independent of control from the operator, and means controlled at the will of the operator in'the first exchange for opening said connection.

17. In a telephone system, a trunkline terminating in a line relay, an impedance coil,

a circuit for said line relay including said trunk line, said impedance coil, and said line relay in series, said impedance coil rendering said line relay nonresponsive to ringing cur,- rent when ringing current is applied to the I trunk line, means for closing a circuit to operate the line relay, and means responsive to the operation of said line relay forshort circuiting said impedance coil thereby directly connecting said line relay with said trunk line.

18. In a telephone system, a first and a sec- 7 0nd exchange, an interconnectingtrunk. line terminating at each exchange in an operators switchboard, a branch at the second exchange connecting said trunk-line to an automatic,

switch in that exchange, means, at each switch may be controlled over'two conduc-.

tors of said trunk'line in series from the switchboard at the first exchange.

19. In a telephone system, two exchanges, I a group of trunks comprisingftwophysical switchboard wherebyv the operator thereat one exchange, and means at the other exchangefor controlling the operation ofsaid switch over said physical'trunksiin series.

20. In a telephone system, a trunk line, asignal at one end of said trunk line operative responsive to the application of alternating current to the other end of the trunk line, an automatic switch, a line relay bridged across the conductors of said trunk line atsai'done end thereof and responsive todirect current impulses sent over said trunk line for controlling the operation of said automatic switch, and means for substantiallypreventing the passage of alternating current through-said line relay when such current-is applied to said trunk line to operate said:

signal.

21. In combination with a two-way trunk line adapted to be signalled'over by means of alternating current applied to either end, a relay bridged across the trunk in serieswith asource 01" direct current, and an'impedance' I in the circuit of said relay for substantially preventing the passage'of alternating cure rent to said relaywhen such current is ap-' plied to the trunk line. i

'22. In combination with'a two-way trunk line adapted to be signalled over bymeans of alternating current applied to either-end, a relay bridged across the trunk lineand opthe trunk lineby way of said jack for an'-- swering. calls [on the trunk line,;andmeans controlled overthetrunk line. I'OYZLH'DOHlkl-tl "erative responsive to a flow of direct current cally connecting, said operators circuit with the trunk line independent of said aclL' E24. lzIn a telephone system',.a trunk line havr. mg twobranches, one branchterminating 1n p p i 's a manual'gack andsi'gnal, theothenbranchv terminating an automatic switch-,meansj controlled over the tru'nlrjline for operating;

eithersaid signal orjsaid switch, an operators circuit adapted to be manually connected to said trunk line via sa1d ack to answer calls on th'ertrunk line, andmeanscontrolledby,

said switch for connecting said operators circuit to the trunk; line independentxof said v ack. i 1 f or 2. i 25 Ina telephone system, three exchanges? hrough tolllines. connecting the. first and;

third exchanges, other toll. lines connecting 'th e'first and second exchangesaalink circuit g 1 3D,

in the secondexchan'geiadapted to be manu- 1 ally connected with a subscribers line, an automatic switch in the second exchange controlled from the first exchange over one of said other toll lines, and means controlled b said switch for connectin said link circuit with any one of said throughtoll lines.

26. In a telephone system, three exchanges, through trunk lines connecting the first and third exchanges, other trunk lines connecting the first and second exchanges, a link circuit in the second exchange adapted to be con nected to a subscribers line, an automatic switch in the second exchange, means for directively operating said switch over one of said other trunk lines to establish a connection between said link circuit and one of said through trunk lines, means for releasing the switch, and means in said link circuit for maintaining said connection intact after saidswitch is released. a

27. In a telephone system, three exchanges, through trunk lines connecting the first and third exchanges, other trunk lines connecting the first and second exchanges, a link circuit in the second exchange adapted to be connected to a subscribers line, an automatic switch in the second exchange, means for directively operating said switch over one of said other trunk lines to establish a connection between said link circuit and one of said through trunk lines, means for releasing the switch, locking means in said link circuit for maintaining said connection intact after said 7 switch is released, and means for reoperating said switch to disable said locking means and to release said connection.

28. In a telephone system, three exchanges, through toll lines connecting the first and third exchanges, normally disconnected branches of said toll lines extending to said second exchange, trunk lines connecting the first and second exchanges, and means in the second exchange controlled from the first exchange over-one of said trunk lines for establishing a connection between the second and third exchanges via one of said toll lines and the branch thereof without affecting the con tinuity of the toll line connected with.

29. A telephone system in which a first and a second exchange are connected by a trunk line terminating at each exchange in an operators switchboard, and also in an automatic switch at the second exchange, in which the V operators at the two exchanges may signal each other by applying alternating current to the trunk line, and in which the automatic switch. is controlled by a line relay bridged across the conductors of said trunk line, characterized in that an impedance is included in the circuit of said line relay to prevent false operations of the line relay when alternating current is applied to said trunk line. 7

XII). witness whereof, I hereunto subscribe my name-this 28th day 'ot April, A. 1)., 1927. Q VIII/TOR, S. THARP. 

